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Coordination and response CIE A Level Biology re ...
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What causes the conformational change in the troponin-tropomyosin complex
calcium ions attach to troponin
What impact does the action potential have on the sarcoplasmic reticulum?
it opens calcium ion channels on the SR which causes calcium ions to floor the sarcoplasm.
What is the name of the endoplasmic reticulum of the muscle
sarcoplasmic reticulum
Why are muscle fibers not usually referred to as cells?
they are multinucleate
Describe the structure of actin?
globular protein molecules linked to form a chain which wrap to form a helical shape; tropomyosin is twisted around the two chains and troponin is also present
Describe the structure of myosin
fibrous protein molecules anchored at the M line of a sarcomere each containing globular heads which point away from the M line
Where is the Z band?
In the middle of the I band
What type of fibers are found in the I band?
Only actin
What type of fibers are found in the H band?
Only myosin
What type of fibers are found in the A band?
myosin and actin
Once Ca2+ binds to troponin what happens to allow muscle contraction?
Troponin tropomyosin moves to expose myosin binding sites on the actin filaments, myosin heads form cross-bridges with thin filaments and the sarcomere shortens
What happens in the muscle fibers after the action potential is initiated?
depolarisation spreads down the T-tubules, channel proteins for Ca2+ open and Ca2+ ions diffuse out of the SR, bind to troponin
What happens after acetylcholine diffuses into the synaptic cleft?
it binds with receptors on the sarcolemma causing Na+ channels to open and Na+ to diffuse in and depolarise the membrane and initiate an action potential
Explain the events in the presynaptic neuron at the neuromuscular junction starting with the arrival of an action potential
diffusion of Ca2+ into neuron causes movement of vesicles containing acetylcholine which diffuses across the synapse to fuse with the presynaptic membrane
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